1. Field of the Invention
Our invention pertains to apparatus for manipulating mechanical heart valve prostheses and in particular, for manipulating heart valve prostheses implanted at the site of the mitral valve.
2. Description of Related Art
Heart valve prostheses may be classified into two general categories: bioprosthetic heart valves and mechanical heart valves. By bioprosthetic heart valves we mean heart valves with generally flexible leaflets comprised of biological tissue. These include leaflets formed of treated human valve tissue (allografts), or of treated porcine or other non-human tissue (xenografts). By mechanical heart valves we mean heart valves made primarily from non-biologic materials, for example, metals, ceramics or polymers. These include ball valves and valves having one, two or more rigid leaflets. One popular valve design for a mechanical heart valve prosthesis includes an annular valve body in which a pair of opposed leaflet occluders are pivotally mounted. The occluders are movable between a closed, mated position, blocking blood flow in an upstream direction, and minimizing regurgitation, and an open position, allowing blood flow in a downstream direction. The annular valve body is surrounded by a sewing ring which permits the surgeon to suture the valve in place at the site of an excised valve.
When a valve is placed within the heart, it must be accurately oriented to maximize its function. Particularly in mechanical heart valves, the orientation of the leaflets is critical since their opening and closing pathways may otherwise impinge on the surrounding cardiac walls, the walls of arteries within which the valve is placed, or the residual valvular structures including the tendeae chordae and papillary muscles. This difficulty becomes particularly acute in the placement of a heart valve in the position of the mitral valve in the heart. When replacing this valve, a surgeon will frequently expose the posterior side of the patient's heart and enter the heart through walls of the left atrium and sometimes through the right atrium. It is desirable to place the valve accurately within the cramped confines of the heart while leaving room for the surgeon to sew the valve in place. Moreover, accurate sizing of the prosthetic heart valve is very important for the long-term viability of the prosthesis. The size of the heart valve can frequently not be determined exactly until the site of the valve has been exposed. Thus, it is a frequent occurrence that a different sized valve may be selected by a surgeon interoperatively.
In the past surgeons most often used a left thoracotomy surgical procedure to reach the heart which allows a straight line of access to the mitral valve. Common practice, however, has shifted away from the thoracotomy which involves resecting a rib and provides poor access to the aorta. Many surgeons today perform a median sternotomy, bisecting the rib cage by sawing the sternum in half. This approach provides clear access to the aorta and right atrium, allowing the surgeon to easily place the patient on by-pass, work on the aortic valve and either the pulmonary or tricuspid heart valve. Unfortunately, this approach does not provide easy access to the mitral valve, forcing the surgeon to reach behind the heart or through the right atrium into the left atrium.